S. Komathi

Fabrication of enzymatic glucose biosensor based on palladium nanoparticles dispersed onto poly(3,4-ethylenedioxythiophene) nanofibers.

A new methodology involving the combination of a soft template (surfactant) and an ionic liquid (co-surfactant) is used to electrodeposit poly(3,4-ethylenedioxythiophene) (PEDOT) nanofibers. Electrochemical deposition of palladium nanoparticles and glucose oxidase (GOx) immobilization are done sequentially into nanofibrous PEDOT to fabricate the modified electrode (ME) (denoted as PEDOT-Pd/GOx-ME). The PEDOT-Pd/GOx-ME displays excellent performances for glucose at +0.4 V (vs. Ag/AgCl) with a high sensitivity (1.6 mA M(-)(1) cm(-2)) in a wider linear concentration range, 0.5 to 30 mM (correlation coefficient of 0.9985). Further, the electrode is insusceptible to the electroactive interfering species.

Fabrication of a novel layer-by-layer film based glucose biosensor with compact arrangement of multi-components and glucose oxidase

Layer-by-layer (LbL) film based glucose biosensor was fabricated with alternative layers of a nanocomposite (comprising of multiwalled carbon nanotubes (MWNTs), Au nanoparticles (Au NPs) and thiol functionalized polyaniline (PANI(SH)) and glucose oxidase (GOx). The successful formation of multilayers was confirmed by UV-visible spectroscopy. The components in the nanocomposite provide adequate electron transfer path between GOx and the electrode. A high value for the rate constant of electron transfer process (27.84 s(-1)) was observed at [GOx/Au-(SH)PANI-g-MWNT](n)/ITO electrode. The [GOx/Au-(SH)PANI-g-MWNT](n) biosensor exhibited high sensitivity (3.97 microA/mM) for the detection of glucose over a concentration range of 1-9 mM with a low detection limit of 0.06 microM.

Bioelectrocatalytic determination of nitrite ions based on polyaniline grafted nanodiamond

Polyaniline chains were grafted onto nanodiamond (PANI-g-ND) through electrochemical polymerization of aniline in the presence of amine functionalized ND. A robust and effective composite film comprising PANI-g-ND/gold particles was subsequently prepared. Cytochrome c was successfully immobilized onto PANI-g-ND/Au film. Field emission scanning electron microscope (FESEM) image of PANI-g-ND/Au reveals the presence of fibrous PANI embedded into ND galleries with uniformly distributed Au clusters (∼1 μm). Direct electrochemistry and electrocatalysis of cyt c were investigated. PANI-g-ND/Au film showed an obvious direct electron transfer between cyt c and the underlying electrode. Cyclic voltammograms revealed that PANI-g-ND/Au/cyt c exhibited an excellent electrocatalysis towards the detection of nitrite ions. Differential pulse voltammetry of PANI-g-ND/Au/cyt c revealed a wide linear concentration range (0.5 μM-3 mM) for current responses, sensitivity (88.2 μA/mM) and low detection limit (0.16 μM) towards the electrochemical detection of nitrite ions.

Efficient visible-light-driven photocatalytic degradation of nitrophenol by using graphene-encapsulated TiO2 nanowires

In this work, a new hybrid nanocatalyst, namely titanium dioxide (TiO2) composite nanowires, encapsulated with graphene (G) and palladium nanoparticles (Pd NPs) (designated as G-Pd@TiO2-CNWs), was prepared. In preparing the nanowires, a combination of electrospinning and hydrothermal approaches was employed. The visible-light-driven photocatalytic performance of G-Pd@TiO2-CNWs was investigated using the reduction of 4-nitrophenol (4-NP) as a model reaction. The results showed that G-Pd@TiO2-CNWs converted nearly 100% of 4-NP under visible light irradiation. The reaction kinetics of the photocatalytic reduction of 4-NP was studied by UV-vis spectrophotometry and the apparent rate constant was determined and compared with those for other supported TiO2 catalysts. Furthermore, the spent G-Pd@TiO2-CNWs could be recovered by simple centrifugation and reused. The work is expected to shed new light on the development of G-incorporated hybrid nanostructures for harvesting light energy and on the development of new photocatalysts for the removal of environmental pollutants.

Fabrication of a novel dual mode cholesterol biosensor using titanium dioxide nanowire bridged 3D graphene nanostacks

Herein, we fabricated a novel electrochemical-photoelectrochemical (PEC) dual-mode cholesterol biosensor based on graphene (G) sheets interconnected-graphene embedded titanium nanowires (TiO2(G)-NWs) 3D nanostacks (designated as G/Ti(G) 3DNS) by exploiting the beneficial characteristics of G and TiO2-NWs to achieve good selectivity and high sensitivity for cholesterol detection. The G/Ti(G) 3DNS was fabricated by the reaction between functionalized G and TiO2(G)-NWs. Cholesterol oxidase (ChOx) was subsequently immobilized in to G/Ti(G) 3DNS using chitosan (CS) as the binder and the dual mode G/Ti(G) 3DNS/CS/ChOx biosensor was fabricated. The electro-optical properties of the G/Ti(G) 3DNS/CS/ChOx bioelectrode were characterized by cyclic voltammetry and UV-vis diffuse reflection spectroscopy. The cyclic voltammetry of immobilized ChOx showed a pair of well-defined redox peaks indicating direct electron transfer (DET) of ChOx. The amperometric reduction peak current (at -0.05V) linearly increased with increase in cholesterol concentration. The G/Ti(G) 3DNS/CS/ChOx bioelectrode was selective to cholesterol with a remarkable sensitivity (3.82μA/cm(2)mM) and a lower detection limit (6μM). Also, G/Ti(G) 3DNS/CS/ChOx functioned as photoelectrode and exhibited selective detection of cholesterol under a low bias voltage and light irradiation. Kinetic parameters, reproducibility, repeatability, storage stability and effect of temperature and pH were evaluated. We envisage that G/Ti(G) 3DNS with its prospective characteristics, would be a promising material for wide range of biosensing applications.

Electrochemical detection of celecoxib at a polyaniline grafted multiwall carbon nanotubes modified electrode

A modified electrode is fabricated by grafting polyaniline (PANI) chains onto multiwall carbon nanotubes (MWNTs) and utilized for the adsorptive reduction of celecoxib (CEL). PANI-g-MWNTs modified electrode appreciably enhances the sensitive detection of CEL in extremely lower concentrations (1x10(-11)M). Square wave stripping voltammogram (SWSV) shows a reduction peak at -1.08V with a high peak current for SW frequency of 100Hz, amplitude of 25mV and step height of 6mV. The high surface area of PANI-g-MWNTs is effectively utilized for the adsorption of CEL to preconcentrate at the electrode. The PANI chains covalently linked to MWNTs mediate the electron transfer processes. The present finding open-up the scope for extending on the use of other conducting polymers grafted MWNTs modified electrodes for the detection of compounds that do not have surface-active properties at conventional electrodes.

A novel multicomponent redox polymer nanobead based high performance non-enzymatic glucose sensor.

The fabrication of a highly sensitive electrochemical non-enzymatic glucose sensor based on copper nanoparticles (Cu NPs) dispersed in a graphene (G)-ferrocene (Fc) redox polymer multicomponent nanobead (MCNB) is reported. The preparation of MCNB involves three major steps, namely: i) the preparation of a poly(aniline-co-anthranilic acid)-grafted graphene (G-PANI(COOH), ii) the covalent linking of ferrocene to G-PANI(COOH) via a polyethylene imine (PEI), and iii) the electrodeposition of Cu NPs. The prepared MCNB (designated as G-PANI(COOH)-PEI-Fc/Cu-MCNB), contains a conductive G-PANI(COOH), electron mediating Fc, and electrocatalytic Cu NPs that make it suitable for ultrasensitive non-enzymatic electrochemical sensing. The morphology, structure, and electro activities of MCNB were characterized. Electrochemical measurements showed that the G-PANI(COOH)-PEI-Fc/Cu-MCNB/GCE modified electrode exhibited good electrocatalytic behavior towards the detection of glucose in a wide linear range (0.50 to 15mM), with a low detection limit (0.16mM) and high sensitivity (14.3µAmM(-1)cm(-2)). Besides, the G-PANI(COOH)-PEI-Fc/Cu-MCNB/GCE sensor electrode did not respond to the presence of electroactive interferrants (such as uric acid, ascorbic acid, and dopamine) and saccharides or carbohydrates (fructose, lactose, d-isoascorbic acid, and dextrin), demonstrating its selectivity towards glucose. The fabricated NEG sensor exhibited high precision for measuring glucose in serum samples, with an average RSD of 4.3% and results comparable to those of commercial glucose test strips. This reliability and stability of glucose sensing indicates that G-PANI(COOH)-PEI-Fc/Cu-MCNB/GCE would be a promising material for the non-enzymatic detection of glucose in physiological fluids.

Polyaniline nanoflowers grafted onto nanodiamonds via a soft template-guided secondary nucleation process for high-performance glucose sensing

Superfine polyaniline (PANI) nanoflowers (NF) with protruded whiskers at the edge of the flowers were produced on the surface of nanodiamonds (NDs) using cetyltrimethylammonium bromide (CTAB) as a soft template and fine tuning the graft co-polymerization conditions. Typically, the amount of amino-functionalized ND (ND-NH2) and the soft template CTAB used in the graft polymerization plays an important role in directing the NF morphology. The correlation between the amount of ND-NH2 and morphology has been discussed in terms of secondary nucleation for PANI growth. More importantly, the ND-grafted PANI (NDx-g-PANI) NF exhibits a superior performance for glucose detection and possesses wider linear concentration range (1–30 mM), low detection limit (0.018 mM), and high sensitivity (2.03 μA mM−1) as compared to most of the enzyme glucose sensors fabricated with either PANI or carbon nanostructures. The results obtained from this study offer scope for future studies on the fabrication of new biosensors with other aniline derivatives and carbon nanostructures.

Course of poly(4-aminodiphenylamine)/Ag nanocomposite formation through UV-vis spectroscopy.

Kinetics of chemical oxidative polymerization of 4-aminodiphenylamine (4ADPA) was followed in aqueous 1 M p-toluene sulfonic acid (p-TSA) using silver nitrate (AgNO3) as an oxidant by UV-vis spectroscopy. The medium was found to be clear and homogeneous during the course of polymerization. The absorbances corresponding to the intermediate and the polymer were followed for different concentrations of 4ADPA and AgNO3 and at different reaction time. The appearance of a band around 450 nm during the initial stages of polymerization corresponds to the plasmon resonance formed by the reduction of Ag+ ions. Rate of poly(4-aminodiphenylamine)/Ag nanocomposite (RP4ADPA/AgNC) was determined for various reaction conditions. R(P4ADP/AgNC) showed second order power dependence on 4ADPA and first order dependence on AgNO3. The observed order dependences of 4ADPA and AgNO3 on the formation of P4ADPA/AgNC were used to deduce a rate equation for the reaction. Rate constant for the reaction was determined through different approaches. The good agreement between the rate constants obtained through different approaches justifies the selection of rate equation.

Strategically functionalized carbon nanotubes as the ultrasensitive electrochemical probe for picomolar detection of sildenafil citrate (Viagra).

The present work demonstrates the utility of the functionalized carbon nanotubes, poly(4-aminobenzene sulfonic acid) (PABS) grafted multiwalled carbon nanotubes, MWNT-g-PABS, as an electrode modifier towards achieving ultrasensitive detection of a model drug, sildenafil citrate (SC). PABS units in MWNT-g-PABS interact with SC, pre-concentrate and accumulate at the surface. The electron transduction from SC to electrode is augmented via MWNT-g-PABS. As a result, the MWNT-g-PABS modified electrode exhibited ultrasensitive (57.7 μA/nM) and selective detection of SC with a detection limit of 4.7 pM. The present work provides scope towards targeting ultrasensitivity for the detection of biomolecules/drug through rational design and incorporation of appropriate chemical components to carbon nanotubes.